Monarch butterfly populations have declined catastrophically, raising welfare questions about the mass mortality events affecting billions of individual insects.
Monarch butterfly welfare raises the same philosophical questions as insect welfare generally, with the additional dimension of mass mortality events that affect billions of individual animals simultaneously. If insects have any capacity for suffering — a scientifically contested but not dismissible question — then the catastrophic population declines and mass mortality events at overwintering sites represent welfare harm on an extraordinary scale. The precautionary principle suggests that preventing mass mortality events is appropriate regardless of the resolution of insect sentience debates. Conservation interventions that restore monarch habitat and reduce mortality from pesticide exposure serve both conservation and potential welfare goals simultaneously. Climate change, which intensifies storm events at overwintering sites, represents a long-term welfare and conservation threat to one of the most spectacular insect migrations on Earth.